The present invention relates to a transistor circuit which is applicable to a circuit for resetting an I.sup.2 L (Integrated Injection Logic) circuit containing linear and digital circuits at a low power source potential.
A conventional reset circuit for initializing a semiconductor integrated circuit at the time when a power switch is turned on, for example, has a circuit configuration as shown in FIG. 1. In this figure a series circuit of resistors R1 and R2 is coupled between a power source Vcc line and a circuit ground line. A potential VA appearing at the junction A of resistors R1 and R2 is applied as a reference potential to one input of a comparator circuit 11. The other input of comparator 11 receives a comparison potential VB which appears at the junction B of a series circuit of a resistor R3 and a capacitor C. The series circuit of resistor R3 and capacitor C is coupled between the power source Vcc line and the circuit ground line. The potential rising speed of potential VA at the junction A is faster than that of potential VB at the junction B. Comparator 11 detects the potentials at the junctions A and B and generates a reset signal RS according to the difference between the rising speed of potential VA and that of potential VB.
A circuit having the abovementioned configuration will operate as follows. As shown in FIG. 2, when a power switch (not shown) is turned on at the time t1, the potential VA of junction A rapidly rises from the ground potential "0" to a prescribed potential "Vcc", while the potential VB of junction B rises slowly. The rising speed of potential VB depends on the time constant C.multidot.R3. When the potential VB exceeds the threshold level or the reference potential VA (e.g., 1/2 Vcc) of comparator 11 at the time t2, the level of output RS of comparator 11 is changed from "0" to "1". In the circuit of FIG. 1, "0" level of output RS is used as the reset signal.
According to the prior art reset circuit as mentioned above, no measures have been taken for operating with a relatively low power source potential (less than about 5 V). Thus, it is practically impossible to adapt the prior art reset circuit to an I.sup.2 L (Integrated Injection Logic) circuit which can operate with a low potential of about 0.7 volts or more. A new reset circuit which can operate with said low power source potential is now in demand.